In an example of related art of technology of classifying a message group and analyzing messages in accordance with the classification results, a classification rule is created based on a feature pattern of each piece of text data with a frequent pattern as an attribute, the frequent pattern detected from a combination of words repeatedly appearing in text data based on the morphological analysis results, and also based on class data specifying a class of text data. In another example of related art, metadata of messages with a frequency of appearance equal to or higher than a threshold is taken as a keyword, a first filter associated with the keyword and a second filter not associated with the keyword are separately provided, and a group of first filters for respective keywords and a group of second filters for respective keywords are created.
Japanese Laid-open Patent Publication No. 2004-240517 and Japanese Laid-open Patent Publication No. 2012-123539 are examples of related art.